The present invention relates to a diagnosis system for a motor vehicle and more particularly to a system where correct data formats and signaling speeds of various types of a control system for the vehicle are provided and a format and speed for a vehicle to be diagnosed is automatically selected.
Recently, a motor vehicle has been equipped with an electronic control system for controlling various components of an engine, such as fuel injectors, thereby improving driveability, exhaust gas emission, fuel consumption, and engine power. The electronic control system controls the components based on information represented by output signals from various sensors for detecting engine operating conditions. Accordingly, if malfunctions of components and sensors occur, the engine does not properly operate.
However, because of the complexity of the electronic control system, it is difficult to immediately find out troubles. Accordingly, a trouble diagnosis device for easily checking the electronic control system should be provided as equipment in an auto shop.
Japanese Patent Application Laid-Open 58-12848 discloses a diagnosis system in which an exclusive checking device is provided for measuring pulse duration of fuel injection and engine speed, and for checking whether idling speed is normal. The checking device is provided for diagnosing only designated specific types of motor vehicles.
However, the data format and the signaling speed of the electronic control systems differ with different types of electronic control systems. In order to diagnose various types of vehicles, it is necessary to equip several types of checking devices corresponding to the respective types of electronic control systems, which is inconvenient in management and uneconomical.
Further, a diagnosis system which stores a plurality of data formats and deals with a plurality of signaling speeds for diagnosing various types of electronic control systems has been proposed. In such a system, a code representing a type of an electronic control system equipped in a vehicle to be diagnosed must be input in the diagnosis system for selecting the data format and the signaling speed. However, it is troublesome work to confirm the corresponding code and to input the code consisting of a plurality of figures. If an erroneous code is input, the correct data format and signaling speed are not selected, so that a proper diagnosis can not be performed.